Multiscale Lithium and Counterion Transport in an Electrospun Polymer-Gel Electrolyte

We explore fundamental lithium ion (Li+) and triflate counterion (CF3SO3-) transport properties within an electrospun UV-cross-linked poly(ethylene oxide) polymer-gel electrolyte. With modulation of cross-linker (10-30 wt %), the fully swollen fibrous framework swells and retains between 1700 and 1200 wt % liquid electrolyte and exhibits room temperature ionic conductivity up to 6 mS cm(-1). Li-7 and F-19 spin-spin relaxation (T-2) measurements reveal the presence of inter- and intrafiber lithium ions, where the long- and short-T-2 lithium ion and counterion components enable quantification of the fractions of free liquid electrolyte between fibers and liquid electrolyte within fibers. Pulsed-field-gradient NMR diffusometry shows increases in lithium and triflate diffusion coefficients with cross-linker content, suggestive of enhanced ion transport within the free liquid electrolyte phase due to a reduction in morphological restrictions. Arrhenius fits to temperature-dependent diffusion experiments show that lithium and triflate values for the activation energy of diffusion (15 and 12 kJ mol(-1), respectively) are identical for ions in pure liquid solutions and for ions within the electrospun gel, showing that the framework does not influence the local energetics of ion transport. The present study thus offers new insights into understanding ion transport properties within lithium-ion battery materials on length scales ranging from sub-nanometer to micrometer scales.